When you start to run, you begin to breathe faster and harder. This increased rate and depth of respiration helps the muscles produce cellular energy and removes the byproducts of increased muscle metabolism. When you stop running, the muscles' energy demand returns to resting levels almost immediately. However, respiration rate takes several minutes to return to baseline due to the muscle cells' need to replace energy and oxygen stores, recover from increased body temperature and restore resting hormone levels.
Respiratory System Function
The respiratory system works in conjunction with the cardiovascular system to deliver oxygen-rich blood to the muscles and remove carbon dioxide from the muscles. When you breathe in air, it goes into your lungs. The oxygen in that air diffuses across microscopic blood vessels --- capillaries --- in the alveoli at the end of your lungs and goes into the bloodstream. This oxygen-rich blood goes to the working muscles, and the oxygen diffuses across the muscle capillaries. The muscles use this oxygen to produce cellular energy. Carbon dioxide, a byproduct of cell energy production, diffuses from the muscle capillaries into the bloodstream, where it travels to the lungs, diffuses into alveoli capillaries, and is exhaled.
Respiratory System During Running
When you run, your aerobic, or oxygen-requiring, muscle metabolism increases to produce cell energy at a faster rate. Additionally, the increased metabolism generates more carbon dioxide and reduces blood pH. The neural system detects the reduced blood pH and activates hormones to increase respiratory rate. This helps remove carbon dioxide and restore pH in the muscles. Respiratory rate plateaus as long as oxygen demands are met, carbon dioxide is removed and the pH-lowering hydrogen ions are neutralized. If you begin to run faster, the increased concentration of hydrogen ions will increase your breathing rate and depth to meet the muscles' demands.
Respiratory System After Running
When you stop running, your muscles do not need to produce as much cell energy as they did while running. However, your respiratory rate remains high for several minutes after running. Although the respiratory system has been supplying oxygen and removing carbon dioxide during exercise, muscle cells will still need oxygen to replenish energy depleted during the run. Additionally, the muscles will still have accumulated carbon dioxide and hydrogen ions that the respiratory system needs to remove. Furthermore, your elevated body temperature and hormone levels keep your metabolic rate high, which increases oxygen demands.
Intensity, Duration and Post-running Respiratory Rate
Your respiratory rate will take longer to return to resting levels after a high-intensity run, as compared to an easy jog. High-intensity running uses anaerobic energy metabolism, which depletes additional energy stores and produces more carbon dioxide and hydrogen ions. The duration of your run may affect your post-workout respiratory rate, although duration likely has a less significant effect than intensity. A 1990 study published in "European Journal of Applied Physiology" exercised subjects at different intensities and durations and measured the amount of oxygen taken in after exercise. They showed that while exercise intensity explains 45 percent of the differences in excess post-exercise oxygen consumption, exercise duration explains only 9 percent. This explains why you may feel more out of breath following an all-out 30-second sprint than after a 30-minute moderate-intensity run.
References
- "Physiology of Sport and Exercise, Fourth Edition"; Jack H. Wilmore, David L. Costill, and W. Larry Kenney, 2008
- "European Journal of Applied Physiology"; The Effect of Exercise Intensity and Duration on the Oxygen Deficit and Excess Post-exercise Oxygen Consumption, C.J. Gore and R.T. Withers, March 1990
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